Our goal is to understand the biochemical mechanisms of microbial plaque formation as they are related to the etiology of caries and periodontal disease in man. Successful microbial colonization of the oral cavity is the consequence of tenacious adherence to oral tissues and physiological adaptation to existing growth conditions. These phenomena involve molecules existing on the surface and in the "external" compartment of oral bacteria. Therefore, two classes of proteins will be studied. These appear to be localized outside the plasma membrane of Streptococcus sanguis strain 34 (Ss34), an isolate from human dental plaque. Ss34 coaggregates specifically in vitro with Actinomyces viscosus strain T14V, an human oral pathogen. Class 1 proteins are bound to cell wall fragments of Ss34 so firmly that they are not removed by exhaustive SDS-polyacrylamide gel electrophoresis. However, the protein is solubilized when cell walls are digested by muramidase. Class 2 proteins are released from intact Ss34 when it is treated with lysozyme under hypotonic, non-lytic conditions to yield "lysozyme extract". The specific aims are to: (a) Establish the profile of surface proteins by immunochemical procedures, enzymatic iodination and electrophoresis; (b) Establish the presence in cells of an "external" compartment by localizing certain enzymes such as glycosyl transferase, hydrolases and carboxypeptidases in the lysozyme extract and protoplast supernatant fluids; (c) Fractionate the wall-linked proteins by electrophoresis and characterize their attachment to peptidoglycan; (d) Compare wall-linked proteins with those of lysozyme extract and of the plasma membrane by immunochemical techniques; (e) Probe the spatial orientation of wall-linked proteins with surface-directed antisera. Because streptococci are early colonizers of the oral cavity and because proteins constitute an important surface feature of these bacteria and especially participate in their attachment to tissues, it is hoped that more detailed knowledge of the role of external proteins in the physiology of Ss34 will permit the rational design of procedures, such as colonization with specific mutants, that can be used to control dental caries and periodontal disease.